The fish tapeworm (
Diphyllobothrium latum
), is the largest parasite that infects humans. Humans become infected when they eat raw or undercooked freshwater fish that contain fish tapeworm cysts.

The infection is seen in many areas where humans eat uncooked or undercooked fish from rivers or lakes, including:

African countries in which freshwater fish are eaten

Eastern Europe

North and South America

Scandinavia

Some Asian countries

After a person has eaten infected fish, the larva begin to grow in the intestine. Larvae are fully grown in 3 - 6 weeks. The adult worm, which is segmented, may reach a length of 30 feet. Eggs are formed in each segment of the worm and are passed in the stool. Sometimes, parts of the worm may also be passed in the stool.

Fish tapeworm infection may lead to vitamin B12 deficiency and anemia.

You will receive medicines to fight the parasites. You take these medicines by mouth, usually in a single dose.

The drug of choice for tapeworm infections is praziquantal. Niclosamide can also be used. You may need vitamin B12 injections or supplements to treat the vitamin B12 deficiency and anemia that can occur with this infection.

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